1. Field of the Invention
The present invention relates to a chemical vapor deposition method, and more particularly to a method for forming a silicon oxide film.
2. Description of Related Art
There has been a conventional chemical vapor deposition method where a silicon oxide film is formed by using tetra-ethyl orthosilicate, Si(OC.sub.2 H.sub.5).sub.4, as a source gas and decomposing it at atmospheric pressure. For example, tetra-ethyl orthosilicate as a source gas and trimethoxy phosphate, PO(OCH.sub.3).sub.3, and trimethoxyboron, B(OCH.sub.3).sub.3, as doping gases are introduced into a chamber, mixed with an ozone gas produced by an ozone generator, and decomposed to form a silicon oxide film doped with phosphorus and boron. Alternatively, the formation of silicon oxide films is performed without using any doping gas [Journal of Electronic Materials. Vol. 19. No. 1 (1990) pp. 45-49].
The conventional method of forming the silicon oxide films in the presence of ozone gas as described above has the following problems. First, it cannot be said that the resultant films are of good quality in spite of so high temperature for forming the films as in the range of 350.degree. to 400.degree. C. This may be attributed to the high decomposition temperature of the source gas rendering the condensation polymerization insufficient, and therefore, even such a temperature as in such range cannot allow production of a high quality silicon oxide film. Secondly, the silicon oxide films produced according to the prior art have a strong internal tensile stress of about 1.times.10.sup.9 dyn/cm.sup.2, and because of the high film forming temperature of 350.degree. to 400.degree. C., a thick film or a multilevel film formed is susceptible to cracks due to thermal stress so that they are unsuited to practical use. Thirdly, owing to the high film forming temperature, for example, when the films are produced on the top of an aluminum wiring, protrusions so-often called hillocks may be produced on the surfaces of the aluminum wirings causing electrical shorts between the wiring and the overlying one, thereby markedly lowering production yield.